add commands_pre steps to lint target so that we guarantee pre-commit is always installed

Author: gnikonorov

CONTRIBUTING.rst

@@ -22,6 +22,8 @@ Preparing Pull Requests
 
    Afterwards ``pre-commit`` will run whenever you commit.
 
+   Note that this is automatically done when running ``tox -e linting``.
+
    https://pre-commit.com/ is a framework for managing and maintaining multi-language pre-commit hooks
    to ensure code-style and code formatting is consistent.
 

tox.ini

@@ -24,9 +24,11 @@ deps =
     pytest53: pytest==5.3.*
     pytest54: pytest==5.4.*
 
-# potentially can add install_command ( see https://tox.readthedocs.io/en/latest/config.html?highlight=skip_install#conf-skip_install )
 [testenv:linting]
 basepython = python3
 commands = pre-commit run --all-files --show-diff-on-failure {posargs:}
+commands_pre =
+    pip install pre-commit
+    pre-commit install
 deps = pre-commit>=1.11.0
 skip_install = True